Glacial erosion sculpts the landscape into remarkable landforms like U-shaped valleys, horns, moraine hills and more. Plucked and abraded glacial erosion processes are key factors.
Glaciers don’t erode rock evenly across their path, creating what is known as the trim line along its sides.
Glacial ice in motion can transform landscapes by dislodging and transporting away rock fragments of all sizes. Over thousands of years, its slow movement combined with its weight can completely alter its path over the landscape.
Erosion carves mountains into shapes such as mountains and valleys, creating valleys, fjords, horns and glaciated valleys as it transports sediment from streams into its path for deposit elsewhere (as can be seen with the bluffs west of Bonner Springs).
As they move, glaciers leave behind mounds of dirt, rocks, and gravel known as moraine that serve as markers to show where it once existed. Furthermore, it may deposit material far away from its source, leaving huge boulders known as erratics in their wake; scientists use this data to track glacier movement. Finally, glaciers deposit finely-grained mixtures of sand, silt, and small rocks known as till, providing scientists with additional tracking opportunities.
As glaciers move over the landscape, they erode and transport rock and sediment from place to place, shaping landforms and altering landscapes as they go. At times they may also deposit sediment unintentionally creating new landforms.
Glacial erratics, which form from glacial erosion and melting processes, can create large-scale landscape changes by altering their shape through erosion.
Glacial erosion can leave behind an unstable landscape that poses geohazards. Cirques and troughs formed through erosion can raise the base level for further processes to work on.
Glacial erosion has an enormous influence on the landscape’s geological composition; yet its exact controls remain an ongoing source of contention. Empirical evidence shows that both geology and climate can impact subglacial erosion rates; although attempts at linking erosion patterns with variables like precipitation or latitude have proven ineffective5.
Glacier erosion produces various landforms, including cirques, whalebacks and rock drumlins – often on an international scale – when accumulation (via new snowfall) exceeds ablation, leading to glacial advance down valleys.
As for abrasion, for it to take place ice must move at its base; otherwise it becomes immoveable and inevitability stops occurring. Furthermore, tools must remain near their point of origin and continuously replenished near it; given how quickly ice retreats it’s impossible to retrieve used tools as they vanish into it and cannot be recovered again.
Although difficult to observe, glacial processes are essential in understanding their environment. Their influence can be particularly noticeable on the environment as they break apart soil macro-aggregates, release organic compounds and mobilize nutrients that get redistributed or mobilized; or even erode rocks by compressing or compressing together rocks together before cracks form in sediment beneath glacier ice; this phenomenon is known as plucking.
The Trim Line
As global warming accelerates, glaciers around the world are retreating rapidly as glacial meltwater runs off into rivers and oceans; faster erosion rates have taken over in their place.
But the meltback is also leading to another form of erosion: one which is difficult to observe. This involves the “trim line”, or boundary between smooth bedrock and hard, compacted regolith.
Glacial erosion leaves behind striking landforms. One classic feature is striations on abraded bedrock surfaces – these subparallel grooves formed by glacier movement scraping against rocks at their bases are like tools frozen into place by glaciers scraping against rock faces; sometimes these grooves can even reach depths of several meters wide and hundreds of meters long! A bowl-shaped glacial cirque, like this image from Glacier National Park shows, also often forms due to glaciers flowing down different sides of mountains by pucking rocks off one side before carrying them down another side – leaving unique landforms behind when these landforms form due to glaciers moving on different sides or through mountains when rocks from one side are carried downhill to be picked up again on another side in this form of formation called glacial cirques!